Disclosed in JPH11-170308A is a valve gate apparatus, which is included in an injection molding machine for injecting a molten resin from an injection port thereof, including a valve for injecting the molten resin, a heater for heating the molten resin within the valve, a center core pin, and a ring gate. According to the valve gate apparatus disclosed in JPH11-170308A, the center core pin is inserted into a center portion of the valve, so that the injection port is formed between an outer circumferential surface of the center core pin and an end portion of the valve. Furthermore, the ring gate is provided at the valve gate apparatus so as to be slidable along the outer circumferential surface of the center core pin and so as to stop a flow of the resin by an outer circumferential surface of an end portion of the ring gate when the end portion of the ring gate is positioned at the injection port. Additionally, the valve gate apparatus disclosed in JPH11-170308A includes a solidified layer delamination-preventing groove portion at the outer circumferential surface of the center core pin so as to be positioned between the vicinity of the injection port and a retracted position of the ring gate.
According to the valve gate apparatus disclosed in JPH11-170308, a solidified layer in a thin film state is formed at the solidified layer delamination-preventing groove portion, which is provided so as to be away from the ring gate.
Generally, a molded object is formed by injecting a material used for a molding injection into a cavity through a hot runner and a gate, which is connected to the hot runner. On the other hand, according to an injection molding method disclosed in JP2003-11171A, an area of an injection molding apparatus corresponding to an end surface of the molded object is used as a gate, so that the material is injected into the cavity from the gate.
According to the injection molding method disclosed in JP2003-11171A, a structure of the hot runner is simplified because the area of the injection molding apparatus corresponding to the end surface of the molded object is used as the gate, so that the material is provided to the cavity through the gate.
Disclosed in JPH11-254488A is a valve gate-type mold apparatus that includes a valve casing, a heater and a valve pin. The valve casing is provided within an accommodation bore formed at a mold body and includes a material passage at an inner portion of the valve casing. The heater is provided at the valve casing. The valve pin is configured so as to open and close a gate provided within the valve casing. Furthermore, the valve gate-type mold apparatus disclosed in JPH11-254488A includes a heat insulating and sealing member, which is fitted into a clearance formed between an end portion of the valve casing and an end portion of the accommodation bore of the mold body positioned so as to correspond to the gate. The heat insulating and sealing member is configured so as to protrude towards the gate relative to the end portion of the valve casing. Furthermore, the heat insulating and sealing member includes a valve pin insertion bore so as to surround an outer circumferential surface of the valve pin.
According to the valve gate-type mold apparatus disclosed in JPH11-254488A, the clearance formed between the end portion of the valve casing and the end portion of the accommodation bore of the mold body positioned so as to correspond to the gate is filled with the heat insulating and sealing member. Accordingly, an amount of a material accumulated within the clearance may be reduced.
However, a clearance (e.g. a space), within which the molten resin is accumulated, may be formed at the heater so as to extend from an end portion of the heater positioned closer to the cavity in a case where the injection port is closed. For example, the solidified layer delamination-preventing groove portion corresponds to such clearance. Therefore, the molten resin may be accumulated within the clearance, and the accumulated resin may be solidified or may be deteriorated because the accumulated resin is exposed to a low temperature than an appropriate temperature in order to maintain a molten state of the material for a long period of time. Accordingly, the deteriorated resin or the solidified resin may be mixed into the molten resin when being injected next time, which may result in deteriorating molding accuracy in shape, external appearance, weight and the like.
Furthermore, according to the valve gate-type mold apparatus disclosed in JPH11-254488A, the heater is provided so as to be away from the gate and further, the heat insulating and sealing material is provided between the heater and the gate. Accordingly, heat generated by the heater is less likely to be transmitted to the gate. Furthermore, a temperature of the molten resin may be extracted by the mold body when the molten resin passes through the gate.
A need thus exists to provide a valve gate for an injection valve which is not susceptible to the drawback mentioned above.